1 Intro

Project title: PFAS exposure of humans, animals and environmental compartments: an evidence review map and bibliometric analysis

In this document I provide the results of my Evidence Review Map (Chapter 1 of my thesis). Results are organized in 3 objectives.

2 Project’s objectives

  • Objective 1 Mapping

What evidence on PFAS has been systematically synthesized?

I aim to reveal what areas in the realm of PFAS health-related and environmental research have been synthesized the most and where syntheses of evidence are lacking.

  • Objective 2 Critical appraisal

How robust are systematic syntheses of PFAS evidence?

I examine the included syntheses for their reporting quality and potential biases, in order to assess reliability of reviews’ conclusions, reveal syntheses that should be re-done, and highlight the aspects of review methodology that need to be improved.

  • Objective 3 Bibliometrics

How is synthesized PFAS evidence connected?

I examine which countries and institutions are mostly involved in secondary PFAS research and what do the networks between these institutions look like.

3 Search and screening outcomes

PRISMA flowchart

  • 109 included systematic reviews (SRs)

However, we have 42 more SRs found during an update search up to end 2022.

4 Objective 1

Mapping: What evidence on PFAS has been systematically synthesized?

  • Humans are the most reviewed subject in SRs on PFAS exposure, with 82 SRs, followed by multiple subjects (12), environmental compartments (8), and animals (7).

  • “Humans” and “toxicity” were the most frequently used MeSH terms across all subjects, followed by “fluorocarbons” and “chemically induced”.

  • Most SRs investigated multiple types of PFAS, with PFOA and PFOS being the most reviewed PFAS types, followed by PFHxs, PFNA, and PFDA.

  • The number of SRs published annually has steadily increased over time, with a significant spike in 2021.

  • Recent syntheses are less likely to include quantitative synthesis through meta-analysis.

  • The increase in published SRs over the years is due to SRs on humans.

  • Reviews after 2019 tend to focus on PFAS and not on POPs in general.

  • PFCA and PFSA are still the two most reviewed groups.

  • PFAS with a short or long carbon chain are less reviewed than PFAS with a medium-length carbon chain.

4.1 Supplementary materials

Species plots:

5 Objective 2

Critical appraisal: How robust are systematic syntheses of PFAS evidence?

  • Most SRs included a statement regarding conflicts of interest and few acknowledged the potential presence of COI.

  • Most SRs reported receiving funding, with the majority funded by non-profit organizations.

  • Most SRs did not make their raw data or analysis code available, limiting the ability to verify findings or replicate analysis.

  • Over 50% of the SRs received poor scores (i.e., 0 or 0.5 scores) on a majority of AMSTAR 2 questions, indicating a need for improvement in the rigor and quality of the literature.

  • The highest scoring assessment questions related to clarity of explanation and reporting of conflict of interest.

  • The lowest scoring questions related to transparency measures, such as reporting sources of funding of the included studies and list excluded studies.

  • Many SRs lacked clear research questions and inclusion criteria, established review methods prior to the conduct of the review, and used a comprehensive literature search strategy.

  • Many SRs also had limited reviewer involvement in study selection and data extraction, and inadequate techniques for assessing the risk of bias and discussing heterogeneity and publication bias.

  • Only half of the recent SRs follow reporting guidelines.

  • Recent SRs are more likely to include a conflict-of-interest statement and a funding statement than earlier reviews.

  • Almost all the reviews are founded by no-profit organizations.

5.1 Supplementary materials

Quality of reviews (AMSTAR2 score) differs according to field of research, publication year, review type, publication source. work in progress

6 Objective 3

Bibliometric analysis: How are PFAS reviews connected?

work in progress

Figures in the main paper:

  1. Heat map of the world showing the number of reviews affiliated with each country. Example:

  1. Chord diagram of the collaborations between affiliate countries. Example: check pdf file

  2. Chord diagram showing connectedness of review subjects (humans, animals, environment)

Plus more analyses in supplementary materials